(a) A ray of light is incident on a surface separating air from a denser medium A of refractive index $\mu_1$. It is then made incident on the parallel surface of another medium B of refractive index $\mu_2$ at the same angle of incidence. If the angle of refraction in the two media are $30^{\circ}$ and $35^{\circ}$ respectively, then in which one of the two media (A or B) will light travel faster and why ? (b) The intensity of the two interfering waves in Young's double slit experiment is $I_0$ each. Find the intensity at a point on the screen where path difference between the interfering waves is (i) $\frac{\lambda}{2}$, and (ii) $\frac{\lambda}{3}$.